The present invention relates to a method and a device for detecting a deflated condition of a tire on a vehicle such as a car or a truck. More particularly, the invention relates to a method and a device capable of reducing cost by the use of wheel speed pulse in an ABS (Anti-lock Braking System) and of detecting simply and reliably simultaneous deflated condition of not less than two wheels at minimum increase of cost by installing a pneumatic pressure detector at a wheel.
Pneumatic pressure of tires greatly influences on the performance of vehicles, especially the deflation of tires has a close relation to safety for drivers. Hence, many systems for detecting a deflated condition of a tire have been proposed. However, these proposals could not realize both high reliability and low cost so that they have not been widely spread. Recently, with the spread of ABS, there has been proposed a system with low cost and high reliability wherein the wheel speed pulse in the ABS is utilized. Although the system reliable to a deflated condition of one tire, it is not reliable to simultaneous deflated condition of not less than two wheels.
In the meanwhile, the device for detecting a deflated condition are classified into several types according to detection methods. One of the devices is of a type which directly detects pneumatic pressure of tires and the other is of a type which detects physical quantity such as deflation amount or revolution number which changes with pneumatic pressure.
The former is more reliable than the latter while the device is complicated and expensive because transmission of signals from a rotating body to a static section is difficult. On the other hand, the latter is simple and cheap while it is less reliable than the former.
Also, in the systems for detecting a deflated condition on the basis of wheel speed, a deflated conditioned of a tire is generally determined by the comparison between the wheel speed pulse of the deflated pneumatic tire and that of the normal pneumatic tire. Accordingly, the pneumatic pressure of at least one tire must be normal, so that the simultaneous deflated condition of all wheels cannot be detected theoretically.
In view of the above state of the art, it is an object of the present invention to provide a method and a device for detecting a deflated condition of a tire for which the cost is low and which has high reliability and can detect simultaneous deflated condition of all wheels on a vehicle.